CR2032 button cell batteries

　　Overview of technologies related to CR2032 button cell batteries fuel gauge

　　Compared with the advancement of electronic and semiconductor technology, handheld and portable devices have physical limits such as size and weight. The most important thing about this restriction is that it imposes restrictions on the energy storage devices of handheld and portable devices, that is, the size and weight of the battery. Of course, the battery capacity is directly related to the battery life of handheld and portable devices. However, this topic will not be discussed excessively here.

　　Since the battery power capacity is fixed (of course, this is only for a fixed time, with long-term use, the battery has the problem of aging; that is, the usable power capacity is less than that of a new battery). The purpose of the fuel gauge is to accurately estimate the remaining battery power no matter what time the battery is used. Furthermore, based on the current energy consumption of the device, the remaining available time can be estimated. From a user's perspective, if we can further estimate how long it will take to watch a movie, how long it will take to make a phone call, how long it will take to hold a video conference, how long it will take to play games, etc. It can be said that it elevates the function of the fuel gauge to the highest level.

　　Below we will further analyze the most important fuel meter technologies:

　　Analysis of main fuel gauge technologies:

　　1. Voltage look-up table method to calculate remaining power

　　Since the development of handheld and portable devices, battery technology has been widely used in these devices. From a practical point of view, the accuracy of the remaining battery power has always been one of the key points required by users. No one wants to see 30% remaining power displayed, but the next second or answer a phone call , or turn on the camera to take pictures, only to end up with a power outage. Of course, this situation often happened in the early featurephone era, mainly because the functions of the device at that time were simple and the energy consumption was relatively small. It was not a problem to use a fully charged battery cell for 3 to 5 days. Therefore, the design of the fuel gauge at that time was very simple. It measured the voltage and determined the remaining power through table lookup or simple calculation.

　　Compared with the era of smartphones, a fully charged battery can only last for one day. If the battery level indicator is still 30%, and the next action causes the device to directly power off, I am afraid that consumers will not be able to accept it.

　　The advantages of the voltage look-up table method are low cost and low energy consumption. The disadvantage is that the accuracy is relatively low, and the SOC will jump up and down as the load changes. When the battery ages, this jump phenomenon will be more obvious.

　　2. Coulomb meter

　　Coulomb meter, as the name suggests, is the accumulation of battery charge. The charging and discharging current is detected through the current-sensing resistor, and the amount of electricity rushed in is the capacity of the battery. The total capacity minus the discharged capacity is the remaining battery capacity.

　　This method is relatively simple to implement and the principle is easy to understand. It is a calculation method that is currently used more frequently. However, it cannot be used as a real battery power calculation. The biggest problem with the solution lies in two points. One is the cumulative error. As time goes by, the error will become larger and larger. The other is that the charging capacity and discharged capacity of the battery are not equal. Under different conditions such as load and temperature, , the capacity difference is even greater. The most typical one is that a battery that is fully charged at room temperature can only discharge very little power at low temperatures.

　　Therefore, the coulomb counter is generally only used as an auxiliary tool for power calculation and needs to be used in conjunction with other equipment or sampling data for correction.

　　3. Calculate the remaining power by detecting voltage, current and temperature, and adding algorithms

　　This is a typical power calculation scheme. Under normal conditions of use, the power is calculated by a coulomb meter, and under specific conditions it is compensated by voltage or temperature. For new batteries, the remaining power can be calculated more accurately, but as the battery ages, the accuracy gradually decreases. This is mainly because the calculation basis of the coulomb counter requires knowing the current total capacity of the battery in advance, and then based on the measured current After calculating the used capacity based on voltage, current and temperature, the remaining power is estimated. However, when the battery ages, the total capacity will decrease. At this time, if the total capacity of the new battery is still used as the basis for calculation, the calculation error of the remaining power will become larger and larger.

　　The advantage of this method is that the initial accuracy is very high, but the disadvantages are:

　　(a) The cost of components is relatively high, and additional processes and equipment are required to correct the current-sense resistor and fully charge and discharge the battery to estimate the initial total battery capacity.

　　(b) As the battery ages, the error will increase.

　　(c) The energy consumption of the solution itself is much higher than that of the voltage detection solution.

　　4. Optimization of voltage detection scheme

　　(a) This solution is mainly optimized for long-term accuracy. The most important step is to model the currently used battery cells in the fuel gauge chip. In theory, whether the battery is new or after aging, its OCV (open circuit voltage) ) curves are all the same. Therefore, the battery model is established to provide a reference for the actual remaining power. At the same time, the temperature rise due to large current discharge is also taken into account to improve the accuracy of long-term power calculation. However, in most applications, the accuracy of this solution can be maintained within the normal range.

　　(b) In addition, in response to the above shortcomings, some manufacturers have added a self-learning calibration calculation function to the fuel gauge to cope with the effects of aging and maintain the accuracy of long-term remaining power.

　　5. Optimization of ordinary current detection solutions

　　Due to the large long-term accuracy error of ordinary current detection solutions, some manufacturers have established "Impedance Track" technology to determine the degree of battery aging based on changes in internal resistance to correct the accuracy of remaining power calculations.

　　Fuel gauge technology comparison

　　Market application status analysis

　　Domestic handheld and portable devices can be roughly divided into two parts, one is smartphones, and the other is tablet computers/MIDs. For applications in these two markets, the main reference designs for these two blocks are currently provided by Ap manufacturers. For example, Qualcomm, Broadcom, MTK, nVIdia, Samsung, Hisilicon, etc. for smartphones, as well as Quanzhi, Actions, Rockchip, Vimicro, etc. for tablet computers/MIDs.

　　Since most domestic handheld and portable device manufacturers must rely on AP manufacturers to provide technical support when developing new products, most of the components used in the original reference designs remain unchanged except for wiring. Therefore, as long as the original reference design uses a fuel meter from a certain manufacturer, or Qualcomm, Broadcom, MTK, etc. use the coulomb meter in their own pMIC, the fuel gauge function is then implemented through the calculation of Ap. Currently on the market, because the original designs of Apple mobile phones and tablets used TI's solutions, TI can be said to be the manufacturer that has been working on fuel gauges for the longest time and has the largest market share. Secondly, because Samsung uses a large number of Maxim's fuel meter solutions, Maxim can be said to retain its second position in the fuel meter market.

　　The rest, whether it is a coulomb counter placed in a pMIC, or a fuel meter with a self-learning function such as Cellwise, are all solutions that have entered the market in the past two years. The most important reason for this trend is that consumers are beginning to demand the accuracy of the device's power indication. This requirement is reflected in the operating systems of all handheld and portable devices (iOS, Android, Windowsphone), as well as various apps. It can also be clearly seen from this trend that fuel gauges are playing an increasingly important role in handheld and portable devices.

　　Conclusion

　　The importance of fuel gauges in handheld and portable devices, especially smartphones and tablet computers/MID applications, has been highlighted as Ap manufacturers add coulomb counters to pMICs to provide fuel gauge functions. But this is just the beginning. Since the fuel gauge is the chip that knows the battery best in handheld and portable devices, how to extend the service life of the battery through this feature will be the next application that can be continued.

　　Furthermore, in the application of handheld and portable devices, smartphones and tablet computers/MID are only one part of them. The application of lithium batteries must have accurate fuel gauge applications, which will be developed at any time. What is now visible is the portable power bank in the consumer market is a good example. The price of a mobile power bank without a fuel meter is probably less than US$100. However, the mobile power supply sold by Lifetrons can be priced at US$240 because it has a battery indicator of 00~99. This difference does not represent the price of the fuel meter, but it represents the value of the fuel meter in the minds of consumers.

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